Recently, plastic materials have been often used for various optical materials, especially for eyeglasses, because of being lightweight, highly tough and easy to be dyed. Most important properties required for optical materials, especially eyeglasses, are a high refractive index and a high Abbe number. A high refractive index allows lenses to be thinner, and a high Abbe number decreases the chromatic aberration of lenses. For the purpose of realizing a high refractive index and a high Abbe number, many polyepisulfide compounds which have a good balance of the refractive index and the Abbe number have been reported (for example, see Japanese Laid-Open Patent Publications Nos. 9-71580, 9-110979 and 9-255781). Optical materials obtained from the polyepisulfide compounds described in these patent publications have realized a high refractive index of 1.7 or greater and a high Abbe number, but a material having a still higher refractive index has been desired.
With such a background, Japanese Laid-Open Patent Publication No. 2001-2783 proposes an optical material using an inorganic compound having a sulfur atom and/or a selenium atom for the purpose of realizing a still higher refractive index. In this case, as described in Japanese Laid-Open Patent Publications Nos. 2004-197005 and 2004-137481, in order to guarantee that the obtained optical material is transparent, a preparation process of a composition of the compound needs to include a preliminary polymerization reaction and degassing. However, during the preliminary polymerization reaction and the degassing, the viscosity of the composition is increased. Especially in the case where the amount of the inorganic compound having a sulfur atom and/or a selenium atom is increased to realize a high refractive index, it is difficult to perform a usual cast polymerization operation including filtration and mold injection, and also the tonality of the obtained material is significantly deteriorated occasionally. For preventing these, Japanese Laid-Open Patent Publications Nos. 2006-348285, 2006-348286 and 2006-348289 propose adding a compound having one SH group, a compound having at least one disulfide bond, or a compound having at least one NH group and/or NH2 group. However, the refractive index of the obtained optical material is about 1.76 at the highest.
Patent Document 1: Japanese Laid-Open Patent Publication No. 9-71580
Patent Document 2: Japanese Laid-Open Patent Publication No. 9-110979
Patent Document 3: Japanese Laid-Open Patent Publication No. 9-255781
Patent Document 4: Japanese Laid-Open Patent Publication No. 2001-2783
Patent Document 5: Japanese Laid-Open Patent Publication No. 2004-197005
Patent Document 6: Japanese Laid-Open Patent Publication No. 2004-137481
Patent Document 7: Japanese Laid-Open Patent Publication No. 2006-348285
Patent Document 8: Japanese Laid-Open Patent Publication No. 2006-348286
Patent Document 9: Japanese Laid-Open Patent Publication No. 2006-348289